The purpose of this study will be in investigate the heterogeneity of expression and regulation of alveolar macrophage surface changes. Subpopulations of alveolar macrophages will be defined by Percoll gradient fractionation. The surface sites of these populations that will be investigated will be Fc (IgG) receptors and surface antigens that are identified by monoclonal antibodies. Using monomeric and aggregated homologous H-3 IgG, equilibrium and kinetic binding assays will enable one to determine binding affinity, number of binding sites, and association and dissociation constants of human and guinea pig alveolar macrophages. Intracellular metabolic factors (protein and glycoprotein synthesis) and extracellular factors related to the lung's environment (surfactant and fibronectin) or infection (N-formyl peptides, bacterial factors, and endotoxin) can be evaluated for their modulating effect on Fc receptors. Modulation of Fc receptors in interstitial lung diseases will be evaluated in guinea pigs and humans. Monoclonal antibodies (63D3 and OKIa) have recently become available that react with human monocyte surface antigens. We have showen in preliminary studies that they also react with alveolar macrophages. The distances between subclasses of Fc receptors or between receptor sites and monoclonal antigen surface sites will be measured by fluorescence energy transfer and the mobility of these sites measured by fluorescence photobleaching recovery. The density defined populations of alveolar macrophages will be tested for adherence, spreading, superoxide production, and accessory cell function to correlate function with surface changes. In addition to further define the importance of the antigenic sites defined by the monoclonal antibodies, the functional effect of incubating human alveolar macrophages with monoclonal antibodies will be tested. The findings in normals will be contrasted to the findings in abnomal conditions (i.e. smoking, sarcoidosis, and idiopathic pulmonary fibrosis in humans and silicosis and berylliosis in guinea pigs). These studies will further enhance our understanding of the hertergeneity of alveolar macrophages in normals and may help to identify changes of maturation and differentiation in disease states.